Structural and physiological responses to ozone in Manna ash (Fraxinus ornus L.) leaves of seedlings and mature trees under controlled and ambient conditions

Leaf-level microscopical symptom structure and physiological responses were investigated in seedlings experimentally exposed to ozone (O₃) in indoor chambers (150 ppb, 8 h d^− 1/7 weeks), and field trees of Manna ash (Fraxinus ornus) exposed to ambient O₃ (max 93 ppb/one growing season). Ozone-induced leaf injury, including leaf reddening and stippling, was observed in both seedlings and mature trees, but the morphology of injury in the stipples differed, being hypersensitive-like (HR-like) in the chamber seedlings and accelerated cell senescence (ACS) in the field trees. In both exposure conditions, the main structural impact of O₃ was on the mesophyll and especially the upper assimilating cell layers. The main physiological impact was on carbon assimilation and on stomatal sluggishness. These effects were not due to stomatal structural injury and were more severe in juvenile compared to mature trees because of environmental (water availability, light) and constitutional (gas exchange capacity) factors and differences in the cell physiology processes (HR-like vs. ACS) triggered by ozone stress. Given the plasticity of plant responses to ozone stress, dose/response relationships for tree seedlings in the indoor chambers cannot be extrapolated to mature trees unless ambient conditions are closely simulated.     

Biomass and nutrient content of sessile oak (Quercus petraea (Matt.) Liebl.) and beech (Fagus sylvatica L.) stem and branches in a mixed stand in southern Belgium

Accurate estimates of the amounts of nutrients immobilised in the organs and tissues of different tree species are of prime importance to make appropriate tree species selection and determine the harvesting regime that will ensure forest sustainability. Sixteen sessile oaks (Quercus petraea (Matt.) Liebl.) (64-129 years; stem diameters: 17-57 cm) and twelve beeches (Fagus sylvatica L.) (43-86 years; stem diameters: 9-50 cm) were destructively sampled from a mixed stand located on an acid brown soil in southern Belgium. Statistical models were developed to investigate the differences in nutrient concentrations between tree species, between aboveground tree compartments of the same species, and between tissues of the same compartment. For stem tissues, vertical concentration profiles were described using a versatile equation. Allometric equations were used to predict biomass and nutrient content of tree compartments based on tree dimensions. Broadly speaking, nutrient concentrations tended to be somewhat higher for oak compared with beech, but the amplitude and the direction of inter-species differences varied greatly, depending on the nutrient and the tree compartment. For both species, living branch nutrient concentrations tended to decrease with increasing branch diameter, except for Ca (oak) and Mg (beech). Nutrient concentrations were consistently higher in bark than in wood; this difference between tissues was quite pronounced for Ca, particularly in the case of oak. The biomass and nutrient content equations were used to investigate the effects of tree species and harvesting regime on nutrient exports at harvesting. For equivalent harvesting scenarios, beech was found to induce higher Mg exports than oak, and inversely for Ca. Assuming stand clear cutting, complete tree harvesting would increase average nutrient exports from 65% (Ca) to 162% (P) compared with a stem-only harvesting scenario. These results provide valuable information in the current context of the more intensive utilization of forest products.     

Trans-generational and neonatal humoral immune responses in West Greenland sledge dogs (Canis familiaris) exposed to organohalogenated environmental contaminants

Previous investigations in the Arctic have suggested OHC (organohalogen contaminant) induced immune toxic effects on e.g. polar bears (Ursus maritimus). We therefore studied the dietary impact from minke whale blubber (Balaenoptera acutorostrata), rich in polyunsaturated fatty acids and OHCs, on the humoral immunity of 7 captive West Greenland sledge dog (Canis familiaris) bitches and their 4 pups constituting a sentinel model species for polar bears. A control group was composed of 8 bitches and their 5 pups all fed pork (Suis scrofa) fat. The study included serum IgG measurements (bitches and pups) and specific immune responses towards tetanus toxoid (bitches) and diphtheria toxoid (pups) as well as influenza virus (pups). The analyses showed that IgG concentrations were non-significantly lowest in exposed bitches and pups (t-test: all p > 0.05). In addition, significant lower antibody response was detected in exposed pups immunized with influenza virus at age 3 months (t-test: both p < 0.05). No clear group differences were found for tetanus toxoid in bitches and diphtheria toxoid in pups. The results suggest that the humoral immune system of sledge dogs may be suppressed by the dietary blubber composition of OHCs and polyunsaturated fatty acids while a larger follow-up study is recommended in order to investigate this relationship further.